Preparation of amides of higher fatty acids



y 1966 J. E. DAVIS 3,253,006

PREPARATION OF AMIDES OF HIGHER FATTY ACIDS Filed Oct. 9, 1962 3Sheets-Sheet l ESTER WATER NH3 I NH3 ALCOHOL L WATER 2 ALCOHOL NH3 WATERAMIDE FIG. I

JERRY E. DAVIS INVENTOR.

BY W cwau ATTORNEY y 1966 J. E. DAVIS 3,253,006

PREPARATION OF AMIDES OF HIGHER FATTY ACIDS Filed Oct. 9, 1962 3Sheets-Sheet 2 60 min.

EFFECT OF WATER ON COMPOSITION AT 30 and 60 min. REACTION TIME OOB O.IOO.I2

AMMONIA AMIDE 0.04 0.06 WATER ESTER RATIO IOO- FIG. 2

JERRY E. DAVIS INVENTOR.

BY W (mun ATTORNEY y 1966 J. E. DAVIS 3,253,006

PREPARATION OF AMIDES OF HIGHER FATTY ACIDS Filed Oct. 9, 1962 3Sheets-She et 3 m -1- 2- E .s' B?- E LLI 3 3 i 5 v D: z o LLI I'- 0. 229l- .1 LJJCL 4 i- 2 Lu 8 E -u.| 6 E ro: LIJ 3 n 3 E81 '22 a: @022 m D-c c a EL LIJ 2 r-o m o -o 1 9 E a: I- w 2 IO [N I l l l l l l I l m o oo o o o o o o o 9 m m w m N FIG, 3

JERRY E. DAVIS INVENTOR.

MW wan ATTORNEY United States Patent M 3,253,006 PREPARATION OF AMIDESOF HIGHER FATTY AGES Jerry Edison Davis, Cincinnati, Ohio, assignor toThe Procter & Gamble Company, Cincinnati, Ohio, a corporation of OhioFiled Oct. 9, 1962, Ser. No. 229,465 7 Claims. ((11. 260-404) Thisapplication is a continuation-in-part of my application Serial No.159,836, filed December 18, 1961, and now abandoned.

This invention relates to the preparation of normal amides of fattyacids having from eight to eighteen carbon atoms. In particular itrelates to a commercially desirable method of synthesis for such amides.

The preparation of fatty acid amides can be accomplished by a variety ofknown methods. In general it can be said that the usual methods possessat least one of three serious drawbacks. Either the method requires along reaction time, the method gives low percentage yields, or themethod requires the synthesis of an expensive intermediate compound. Forexample, the common method of synthesis is to allow ammonia and fattyacid to react under anhydrous conditions. This permits almost completeconversion, but requires a reaction time of as much as several days.Similarly, other methods have used expensive intermediates such as acidhalides which react with ammonia to form corrosive inorganic acids aswell as the desired amide.

Accordingly, it is an object of this invention to provide an efficientmethod of synthesis for normal amides of fatty acids.

It is a further object of this invention to provide such a method ofsynthesis which will give a high percentage yield of amide with a shortreaction time.

It is a still further object of this invention to provide such a methodof synthesis that does not require the use of expensive intermediatecompounds.

It is another object of this invention to provide a commerciallydesirable, continuous process for the production of normal amides offatty acids.

The process of this invention involves reacting either (1) a fatty acidhaving from eight to eighteen carbon atoms, (2) an ester of said fattyacid with an alcohol having from one to four carbon atoms, or (3) ananhydride of said fatty acid, With ammonia in the presence of water inan amount from 50% to 200% by weight of the amount of water needed tosaturate the equilibrium reaction mixture. The reaction is maintained ata temperature in the range of from about 320 F. to about 550 F.,preferably 420 F. to 470 E, and the reaction is conducted in a closedvessel at a pressure which is maintained above 1000 pounds per squareinch gauge, preferably above 2000 pounds per square inch gauge.

FIGURE 1 of the drawing is a flow diagram of the process of thisinvention in its preferred aspects of a continuous process, ashereinafter more fully described.

FIGURE 2 of the drawing is a plot of the percentage yield of ammoniaamide against varying water-ester ratios for a reaction of the methylester of middle cut coconut fatty acids, hereinafter defined, withammonia at a temperature of 425 F. and a pressure of about 2,000 poundsper square inch, for varying water-ester ratios.

FIGURE 3 of the drawing is a plot of the percentage yields of totalamide and methyl amide against temperature for the reaction of FIGURE 2at a constant waterester ratio of 0.097.

It will be understood that within the aforementioned ranges there willbe optimum conditions depending upon the particular reactants used andthe practical limitations 3,253,005 Patented May 24, 1966 availability.The preferred reactant of applicant is the methyl ester of a fractionderived from coconut oil having an approximate composition such that 2%of the fatty acids have 10 carbon atoms, 66% have 12 carbon atoms, 3%have 14 carbon atoms and 9% have 16 carbon atoms. The fatty acids arefractionated by distillation most easily when in the form of theirmethyl esters.

The fatty acid groups can be either saturated or unsaturated. Examplesof suitable fatty acid groups include the groups from caprylic acid,capric acid, lauric acid, myristic acid, palmitic acid, stearic acid,palmitoleic acid, oleic acid, linoleic acid, and mixtures of the fattyacids derived from natural fats and oils such as coconut oil, tallow,palm kernel oil, soybean oil, whale oil, fish oil, tall oil, and othernatural oils Whether derived from animal, vegetable or marine sources.

Sufiicient ammonia (NH is used in the reaction to achieve and maintainthe partial pressure hereinafter more fully described.

The optimum water level, which is highly critical to the process of theinvention, is that amount which will just exactly saturate theequilibrium mixture, and desirable results are achieved When 50% to 200%of this amount is employed. Although it is not desired to be bound bytheory, it is believed that the reaction under these conditions proceedsas follows, using fatty acid as an example. [The other possiblereactants (e.g., monohydric alcohol esters or anhydrides) will hydrolyzein water to form the fatty acid and, in the case of fatty acid esters,some impurities (e.g., the alcohol).]:

NH (Vapor phase) :2

RC EN H20 0 ll (RC having from 8 to 18 carbon atoms) The first step inthe reaction is the formation of ammonium soap which quickly changes toeither fatty acid and ammonia or fatty acid amide and water. Theselatter two changes are competing reversible reactions. The ammonia inthe liquid phase is also in equilibrium with the ammonia in the vaporphase. The amide can also be dehydrated to form a nitrile.

By means of these theoretical equations it is possible to explain manyof the effects of changing the important independent variables oftemperature, pressure, water concentration, and the effect of the mixingof the reactants.

The reaction vessel will ideally contain only two phases, one vapor andone liquid. The vapor phase will contain ammonia, water vapor, and anyvolatile alcohol which is present as a result of using esters as rawmaterials. The liquid phase will contain the raw material (e.g., fattyacid, ester, and/or anhydride), free fatty acid or ammonium soap, thedesired amide, water, alcohol when esters are used as raw materials,ammonia, and impurities such as nitriles and substituted amides. Whenmore than the amount of water necessary to saturate this fatty phase isused, a second aqueous phase forms containing a ma jor amount ofammonium soap, as will hereinafter be dis 6 cussed, and minor amounts ofthe other materials in the fatty phase.

The concentration of ammonia in the liquid fatty phase is importantsince by the presence of an excess of ammonia the formation of fattyacid from ammonium soap is desirably kept at a minimum. Since ammonia isformed at the same time as the fatty acid in the decomposition ofammonium soap, a large concentration of ammonia in the liquid fattyphase will drive the reaction in the opposite direction to form ammoniumsoap. This is desirable since this ammonium soap will then change tofatty acid amide and water. Only the ammonium soap in the liquid fattyphase is effective in this portion of the reaction.

The water catalyzes the reaction in which the ammonium soap isdehydrated to form amide. The variation of amide production withreaction-mixture water content is shown in FIGURE 2. Increasing watercon tent increases the production of amide up to a certain point andthereafter an increase in water content causes a gradual decline in theamount of amide produced. The rate of this soap-dehydration reaction isincreased relative to the rate of the reaction in which the amide isdehydrated to form the nitrile to such an extent that nitrile formationcan .be minimized while maintaining a high yield of amide. Nitriles arehighly reactive and may react with such minor ingredients in a detergentcomposition as perfumes or optical brighteners. Consequently, they are ahighly undesirable by-product in an amide which is to be used in adetergent composition. Also, since nitriles are responsible to a largeextent for undesirably coloring amide, the product of the process ofthis invention is much Whiter than an amide product prepared withoutobserving the essential water requirements. It is impossible to formamides without forming nitriles; the process of this invention, however,minimizes this inevitable nitrile formation.

The presence of water in the liquid fatty phase also promotes thesolubility of ammonia in the liquid fatty phase. Therefore, the use, inthe reaction, of the maximum amount of water which is soluble in theliquid fatty phase is desirable. However, water in excess of that neededto saturate the liquid fatty phase will form a new liquid aqueous phasewhich will become saturated with ammonium soap. This ammonium soap insuch a new liquid aqueous phase does not form amide and thus excesswater in the reaction is to be avoided.

The amount of water needed to saturate the reaction mixture can bedetermined fairly closely by determining the saturation points of themajor constituents (amide, fatty acid, etc.). This can be done byinjecting various amounts of water into the fatty material in a closed,pressurized container with agitation until the point where an increasein the amount of water present does not give a corresponding increase inpressure, thereby indicating the formation of a separate aqueous phase.The amount of water in the fatty liquid phase at that point can then bedetermined by analysis.

The reaction of this invention can be conducted at a temperature in therange of about 320 'F. to about 550 F. and Within this range is anoptimum temperature. An increase in reaction temperature from atemperature below the optimum temperature initially permits an increasein the equilibrium ratio of fatty amide tov fatty acid by increasing theamount of water which can be dissolved in the liquid fatty phase whichin turn permits a greater amount of NH to dissolve in the liquid fattyphase. However, the decreasing solubility of ammonia in water (at ahigher temperature) soon counteracts the effect of the increase inamount of water present in the liquid fatty phase and, consequently, anincrease in temperature then lowers the equilibrium concentration ofammonia in the liquid fatty phase. This in turn lowers the equilibriumconcentration (andyield) of fatty amide. Also, additionalfactorsto beconsidered are ,(1) that increasing temperature promotes the formationof undesirable products such as nitriles and contributes to a colorationof the product (temperatures above about 550 are bad for this reason),and (2) that the equilibrium constant for formation of amide appears todecrease With increasing temperature (according to proposed theory).Therefore, for any given pressure there is an optimum temperature,within the range of about 320 F. to 550 F., because of the equilibriumconstant, and these water and ammonia solubility considerations. Theoptimum temperature is primarily determined by the solubility of ammoniain the liquid fatty phase which in turn results in the maximum yield ofamide. For a pressure of about 2000 pounds per square inch gauge, forexample, the optimum temperature is about 425 'F. When the reactants arethe methyl esters of fatty acids derived from coconut oil and ammonia,The variation of amide yield with temperature is shown in FIGURE 3.There is a temperature at which a maximum yield occurs and temperaturesabove and below this temperature result in poorer yields when the samepressure and Water content are used.

The reaction pressure at any given reaction temperature is proportionalto the partial pressure of ammonia vapor present in the reactionmixture. Therefore, increasing reaction pressure increases ammoniaconcentration in the liquid fatty phase which increases the fatty amideyield. As noted above, the reaction pressure should be more than 1000pounds .per square inch. There is a pressure for given reactants where asubsequent increase in pressure does not give a corresponding increasein percentage yield of amide. This optimum pressure is preferably aboveabout 2000 pounds per square inch gauge. Higher pressures can be usedbut are not necessary.

The effect of thorough mixing is to promote the rate of solution of theammonia gas by mixing the vapor into the liquid fatty phase. This isvery important since reaction time is lengthened by inadequate mixingand formation of undesirable side products is promoted. Thus, thereaction mixture should be agitated to achieve optimum results. Thereaction of this invention usually takes from about 30 minutes to aboutminutes.

The volatile impurities (e.g., methyl alcohol, water and ammonia) in thereaction product can be removed by known methods such as flashdistillation after first cooling the mixture to prevent hydrolysis ofthe amide to ammonia soap and/or fatty acid. The method of purificationchosen will depend to a certain extent upon the size of the operationand whether the process is a continuous or batch type operation. Thetype of purification is in general not critical, however, due to theexcellent percentage conversion of fatty acid to fatty amide which canbe achieved with the process of this invention.

When the basic reactant is an ester of the fatty acid with an alcoholcontaining one to four carbon atoms such as methyl ester (all alcoholsherein are monohydric alcohols), another reaction, in addition to thosedescribed abtgve, must be'considered. This reaction is postulated to e:

This N-methyl (or N-alkyl) amide, although technically a byproduct, isuseful as a suds and detergency builder for anionic detergents.Therefore, the product of the instant .process when a methyl ester is astarting material, consisting of a major amount of ammonia amide and aminor amount of N-methyl amide, is extremely useful as 'a detergentbuilder. Due to its relative lack of color and the small amount ofnitrile present, this mixture is extremely desirable. FIGURE 3 shows therelationship of N-methyl amide production to temperature. The amount ofN-methyl amide increases with an increase" in temperature if the othervariables such as pressure and water content are held constant.

The speed with which the instant reaction occurs makes it relativelyeasy to adapt it to a continuous process. Referring to FIG. '1, thebasic reactants are mixed and run through a preheater 1 which raises thetemperature of the mixture to the reaction temperature. The reactionmixture is then run through a tubular reactor 2 at a rate which willprovide sufficient turbulence. The reactor should be long enough to givea sufficiently long reaction time to achieve equilibrium. The tubularreactor 2 can be baffled to prevent back mixing if the flow rate is notsufiiciently fast. The reaction mixture is then run through a cooler 3and subsequently the amide is substantially separated from the reactionmixture in a stripper 4 by flash distillation of the volatile components(e.g., ammonia, Water, and other organic volatiles, if any). If desired,the volatiles may then be subjected to distillation in a still 5 torecover the ammonia and other valuable by-products of the reaction.

The process and its advantages are demonstrated by the followingexamples.

EXAMPLE I In Example I, all runs were made with the methyl esters offatty acids derived from middle-cut coconut oil and having anapproximate distribution of carbon chain lengths as follows: C 2%; C66%; C 23%; and C ,*9%. 291 grams of this methyl ester and alternatelyeither 45 or 114 grams of water were charged to a one liter autoclave.The 45 grams represents theoretical saturation of the reaction mixtureat 450 F. and the 114 grams represents theoretical saturation at 550 F.The reaction mixture was heated to the desired temperature, sufficientanhydrous ammonia was added to produce the indicated pressures, and thereaction mixture was stirred by means of a turbine agitator in thebafiied autoclave. The following table summarizes the results of runsunder varying conditions of water level, temperature, pressure, andtime. The abbreviation FA stands for fatty acid and the abbreviation Astands for the amides of the fatty acid. The percentages are by weightof the organic portion of the reaction mixture. The balance of theorganic portion in each run is unreacted methyl ester, impurities whichwere in the methyl ester, and fatty nitrile, the dehydration product ofamide. These impurities are generally less than one percent of themethyl ester as charged to the autoclave.

Table .H1'gh pressure experiment As can be seen from the preceding data,operation at a Water level near the saturation point of the reactionmixture gave generally higher percentage yields of amide. Both too muchand too little water gave generally decreased yields. An increase intemperature above 450 F. also led to a decrease in percentage yield ofamide and an increase in pressure above 1800 pounds per square inchgauge gave esssentiallly no increase in percentage yield under optimumconditions of water content and temperature. A similar run was made at1800 pounds per square inch gauge, grams of water, 425 5., and minutesreaction time. This run had an organic portion of the reaction productwhich was 91% by weight fatty amide and 5% by weight fatty acid. As canbe readily seen, there is little difference between 425 F. and 450 F.and, therefore, about 425 F. is preferred for economic reasons. Whencaprylic, capric, lauric, myristic, palmitic, stearic, oleic, linoleicacids or their ethyl esters, propyl esters, butyl esters, anhydrides ormixtures thereof are substituted in the previous reactions (in molarequivalent amounts based on fatty acid), substantially equivalentresults are obtained. Also, when the methyl esters of the pure fattyacids hereinbefore mentioned or mixtures other than those derived fromcoconut oil are substituted in the previous reactions (in molarequivalent amounts based on fatty acid), substantially equivalentresults are obtained.

EXAMPLE II A 3 /2inch diameter thermally insulated tube was used as areactor in conjunction with a preheater. A continuous reaction was runin which 750 parts by weight of the methyl ester of Example I, 125 partsby weight of anhydrous ammonia, and 125 parts by weight water werepumped through the reactor at a rate of 1340 pounds/ hour-square feet.The temperature in the reactor was about 430 F. and the pressure wasabout 2000 pounds per square inch gauge. A sample of the reactionmixture taken after the reactants had traversed eight feet of thereactor yielded 79% amides and 5% fatty acid, all percentages being byweight of the organic portion of the reaction mixture. A sample takenafter the reactants had traversed 10.5 feet of the reactor yielded 87%amides and 5% fatty acid, all percentages again being by weight of theorgnic portion of the reaction mixture. Since even the larger reactorlength corresponds to a reactor time of only about 15 minutes in a batchprocess, the product from longer reactors will approach the equilibriumyields of Example I under optimum conditions.

EXAMPLE III Into the reactor of Example II, a mixture of 800 parts ofthe methyl ester of Example I, parts anhydrous ammonia, and 130 partswater were charged at a rate of 1130/pound/hr.-square feet at atemperature of 430 E, and a pressure of 2000 pounds per square inchgauge. Samples taken after eight feet and 10.5 feet of the reactor hadbeen traversed gave respectively 74% amides and 3% fatty acid, andamides and 4% fatty acid. Although not wishing to be bound by theory, itis felt that the slightly lower yields under these conditions are due tothe difference in mixing. The faster fiow rate of Example 11 gave bettermixing and consequently better yields.

The products prepared by the reactions of Examples I, III and III, werefound to be outstanding as suds enhancing and suds stabilization agentswhen used at a 2% level in a granular detergent composition containing17.5% of a mixture of sodium dodecyl benzene sulfonate and sodium talloWalkyl sulfate as active detergent ingredients and 50% sodiumtripolyphosphate. Fatty acid amides prepared by the reaction of thisinvention can also be used as water proofing agents and as intermediatesin preparing amines or sulfonated amides. The latter compounds are usedas wetting, detergent and emulsifying agents.

What is claimed is:

1. The process of preparing a normal amide of a fatty acid having fromeight to eighteen carbon atoms comprising the step of reacting, withagitation, a material selected from the group consisting of (1) fattyacids having from eight to eighteen carbon atoms, (2) the anhydrides ofsaid fatty acids and (3) the esters of said fatty acids with alcoholsselected from the group consisting of methyl, ethyl, propyl and butylalcohols with ammonia in the presence of water in an amount from 7 about50% to about 200% of the amount of water needed to saturate theequilibrium reaction mixture, at a temperature of from about 320 F. toabout 550 F. and a pressure of more than 1000 pounds per square inchgauge, the temperature and pressure being adjusted to provide a maximumconcentration of ammonia in the liquid fatty phase of the reactionmixture.

2. The process of claim 1 wherein the reactants are the methyl esters offatty acids derived from coconut oil.

3. The process of claim 1 wherein the temperature is about 425 F. andthe pressure is about 2000 pounds per square inch gauge.

4. The process of claim 1 wherein the equilibrium mixture is justsaturated with water.

5. A continuous process for preparing a normal amide of a fatty acidhaving from eight to eighteen carbon atoms comprising the steps of (I)forming a reaction mixture by mixing a material selected from the groupconsisting of (1) fatty acids having from eight to eighteen carbonatoms, (2) the anhydrides of said fatty acids, and (3) the esters ofsaid fatty acids with alcohols selected from the group consisting ofmethyl, ethyl, propyl and butyl alcohols with ammonia and water in anamount from about 50% to about 200% of the amount of water needed tosaturate the equilibrium reaction mixture; (II) preheating the mixtureto a temperature of from about 320 F. to about 550 F. with a pressure ofmore than 1000 pounds per square inch gauge; (III) passing the hotmixture through a tubular reactor of sufiicient length to allow thereaction to reach essentially equilibrium; (IV) cooling said reactionmixture; and (V) separating the volatile components from said reactionmixture.

6. The process of preparing a normal amide of a fatty acid having fromeight to eighteen carbon atoms comprising the step of reacting, withagitation, a material selected from the group consisting of (1) fattyacids having from eight to eighteen carbon atoms, (2) the auhydrides ofsaid fatty acids and (3) the esters of said fatty acids with alcoholsselected from the group consisting of methyl, ethyl, propyl, and butylalcohols, with ammonia in the presence of water in an amount from aboutto about 200% of the amount of water needed to saturate the equilibriumreaction mixture, at a temperature of from about 320 F. to about 550 F.and a pressure of more than 1000 pounds per square inch gauge.

7. The process of preparing a normal amide of a fatty acid having fromeight to eighteen carbon atoms comprising the step of reacting, withagitation, the esters of fatty acids having from eight to eighteencarbon atoms with alcohols selected from the group consisting of methyl,ethyl, propyl and butyl alcohols with ammonia in the presence of waterin an amount from about 5 0% to about 200% of the amount of water neededto saturate the equilibrium reaction mixture, at a temperature of fromabout 320 F. to about 550 F. and a pressure of more than 1000 pounds persquare inch gauge, the temperature and pressure being adjusted toprovide a maximum concentgation of ammonia in the liquid fatty phase ofthe reaction mixture,

References Cited by the Examiner UNITED STATES PATENTS 11/1936 Ralstonet al. 260404 XR OTHER REFERENCES CHARLES B. PARKER, Primary Examiner.

1. THE PROCESS OF PREPARING A NORMAL AMIDE OF A FATTY ACID HAVING FROM EIGHT TO EIGHTEEN CARBON ATOMS COMPRISING THE STEP OF REACTING, WITH AGITATION, A MATERIAL SELECTED FROM THE GROUP CONSISTING OF (1) FATTY ACIDS HAVING FROM EIGHT TO EIGHTEEN CARBON ATOMS, (2) THE ANHYDRIDES OF SAID FATTY ACIDS AND (3) THE ESTERS OF SAID FATTY ACIDS WITH ALCOHOLS SELECTED FROM THE GROUP CONSISTING OF METHYL, ETHYL, PROPYL AND BUTYL ALCOHOLS WITH AMMONIA IN THE PRESENCE OF WATER IN AN AMOUNT FROM ABOUT 50% TO ABOUT 200% OF THE AMOUNT OF WATER NEEDED TO SATURATE THE EQUILIBRIUM REACTION MIXTURE, AT A TEMPERATURE OF FROM ABOUT 320*F. TO ABOUT 550*F. AND A PRESSURE OF MORE THAN 1000 POUNDS PER SQUARE INCH GAUGE, THE TEMPERATURE AND PRESSURE BEING ADJUSTED TO PROVIDE A MAXIMUM CONCENTRATION OF AMMONIA IN THE LIQUID FATTY PHASE OF THE REACTION MIXTURE. 